1. Field of the Invention
The present invention relates to a toner composition used, for example, as dry toner for developing an electrostatic latent image.
2. Description of Related Art
A toner using a binder resin as the major component and containing a pigment, a charge controlling agent, an external additive or the like has conventionally been used as a toner for a printer employing an electrostatic latent image developing system.
For example, in a printer employing an electrostatic latent image developing system as shown in FIG. 7, this type of toner T may be fed off from a tank 1 by a supply roller 2. After a toner layer formed on a developing roller 3 is made uniform by a blade 7, the toner T is applied to the surface of a photoconductor 4.
The surface of the photoconductor 4 is charged so as to correspond to a certain image pattern by a laser scanner unit 5 and a corona unit 6, while the toner T is charged to a polarity opposite to that on the surface of the photoconductor 4. The toner T is therefore attracted onto a portion charged on the photoconductor 4, but not to portions which are not charged. Namely, the toner T is dispersed so as to correspond to the certain image pattern (charge pattern) on the surface of the photoconductor 4.
A medium 9 such as paper or the like is then pressed against the photoconductor 4 via an image transfer roller 8 so that the toner image may be transferred onto the medium 9. Heat is then applied to the toner T by a fusing roller 10 so that it is melted and fused on the surface of the medium, thus accomplishing printing of the image.
Because of such applications involved, toner is required of a strength (mechanical strength) and durability of a level sufficient to ensure that it is not crushed, or softened to stick to a roller or the photoconductor of the printer during a printing process.
It is often the case with toner, for the purpose of controlling the amount of charge of toner, that a charge controlling agent is treated and a substance such as hydrophobic silica or the like is externally added to the surface of toner. If the toner lacks in adequate strength, however, the charge controlling agent or the external additive could be embedded in toner, causing the toner to be charged insufficiently. As a result, the toner distribution pattern on the surface of the photoconductor does not accurately correspond to the charged pattern of the photoconductor, resulting in print quality being degraded.
As a solution to this problem, the degree of crosslinking of the binder resin that makes up toner has been enhanced and a gel percentage increased, thereby enhancing strength of toner.
When printing is done on a transparent medium such as OHP transparencies using toner having a color other than black (color toner), a layer made up of toner fused onto the surface of the transparent medium (a toner layer) is required to have a high light transmission.
The type of toner having a high gel percentage is, however, not melted sufficiently even when heat is applied thereto during a fusing process. As a result, the surface of the toner layer after the fusing process is irregularly shaped because an original shape of powder is left unchanged.
If such a type of toner is used to print on a transparent medium, the toner layer scatters rays of light because of its irregular surface shape, thus presenting a-problem of poor light transmission.
In view of the foregoing, it is therefore an object of the invention to provide a toner composition that offers a high light transmission when printing is done on a transparent medium, in addition to a superb strength and durability.
To achieve the foregoing object, a toner composition according to one aspect of the invention comprises at least one kind of binder resin and has a gel percentage of 2 to 15% and a flow-out starting temperature of 80 to 120xc2x0 C.
Since the toner composition according to the invention has a gel percentage of 2% or more, it offers a sufficiently high strength and durability and is never crushed or softened to stick to a roller or a photoconductor of a printer during a print process.
Further, since the toner composition according to the invention has a gel percentage of 15% or less, it is difficult to become brittle and is less likely to crack during a print process.
In terms of preventing the toner composition from becoming brittle, it is even more preferable that the gel percentage be 8% or less.
In the case where the toner composition according to the invention is, for example, transferred to a medium and fused by applying heat thereto, the toner composition according to the invention is melted sufficiently thanks to a low flow-out starting temperature of 120xc2x0 C. or lower thereof and a layer made up of the toner composition (a toner layer) formed on the surface of the medium after the fusing process has a smooth surface shape.
If printing is done on, for example, a transparent medium such as OHP transparencies or the like, using the toner composition according to the invention, therefore, the toner layer, because of smoothness of the flat surface involved therein, allows a large part of an incidence light to pass therethrough without allowing it to disperse, thus offering a high light transmission. The toner composition according to the invention is therefore superior as a color toner used with a transparent medium.
Since the flow-out starting temperature of the toner composition according to the invention is 80xc2x0 C. or higher, toner melted during fusing can be prevented from sticking to a fusing roller. During any time other than fusing, the toner composition is not softened, making it easy to handle.
A gel percentage refers to a percentage of a portion that remains solid to that melted away of, for example, a solid substance (sample) which has been immersed in a certain solvent. Suppose, for example, A g of a sample is placed in a certain solvent (e.g., tetrahydrofuran) and we have B g left as solid without being dissolved. Then, B/A is the gel percentage.
The flow-out starting temperature refers to a temperature at which a solid substance is softened to start exhibiting fluidity.
For example, a solid substance-(sample) is placed in an apparatus (e.g., the flow tester recommended by the Society of Polymer Chemistry manufactured by Shimadzu Corporation) having a restricted outlet (e.g., a nozzle with an orifice diameter of 1 mm and a length of 10 mm) and capable of applying a predetermined load (e.g., 10 kg/cm2) to the sample by means of a plunger; when the sample is heated at a constant rate (e.g., 6xc2x0 C./min.) with the load kept applied thereto, the sample is eventually fluidized to start flowing out through the outlet, which, in turn, causes the plunger to start lowering. The temperature at which the plunger starts lowering may be considered as the flow-out starting temperature.
The toner composition according to the invention may contain components, for example, a dye, pigment, organic finely divided powder, charge controlling agents hydrophobic silica, conductive titanium oxide, and the like, in addition to the binder resin. It should be noted that more than two kinds of dye, pigment, organic finely divided powder, charge controlling agent, hydrophobic silica, conductive titanium oxide, and the likes may be used.
The hydrophobic silica and the conductive titanium oxide have the effect of, for example, improving fluidity of the toner composition or uniformity in charging, respectively.
Typical types of hydrophobic silica include silica subjected to surface treatment using dimethyldichlorosilane, dimethyl polysiloxane, hexamethyldisilazine, amino-silane, and amine. Commercially available silica products include, for example, H2000, H3004, HVK2150, and the like manufactured by Nippon Wacker Co., Ltd. and R974, RY200, RX200, RX300, RA200H, REA200, and the like manufactured by Nippon Aerosil Co., Ltd.
As the conductive titanium oxide, it is preferable that titanium oxide having undergone surface treatment using tin oxide-based semiconductor or indium oxide-based semiconductor be used. It is particularly preferable that the conductive titanium oxide have a resistance value of about 1 to 50 xcexa9xc2x7cm and a BET area/weight ratio of about 5 to 70 m2/g. Example commercially available products include EC-100, EC-210, EC-300, and EC-500 manufactured by Titan Kogyo Kabushiki Kaisha.
A toner composition according to another aspect of the invention, contains at least one kind of binder resin and has a gel percentage of 2 to 15% and a xc2xd-method temperature of 100 to 145xc2x0 C.
Since the toner composition according to the invention has a gel percentage of 2% or more, it offers a sufficiently high strength and durability and is never crushed or softened to stick to a printer part during a print process.
Furthermore, since the toner composition according to the invention has a gel percentage of 15% or less (more preferably 8% or less), it does not become brittle and thus never cracks during a print process.
In addition, since the toner composition according to the invention has a xc2xd-method temperature of 140xc2x0 C. or less, it melts sufficiently well when subjected to a process of fixing it onto the surface of the medium and the surface of a toner layer after the fusing process is smooth.
When printing is done on, for example, a transparent medium such as OHP transparencies or the like, using the toner composition according to the invention, therefore, the toner layer exhibits a high light transmission thanks to smoothness of the flat surface involved therein.
The toner composition according to the invention is therefore superior as a color toner used with a transparent medium.
Since the xc2xd-method temperature of the toner composition according to the invention is 100xc2x0 C. or higher, toner melted during fusing can be prevented from sticking to a fusing roller. During any time other than fusing, the toner composition is not softened, making it easy to handle.
The xc2xd-method temperature may be defined, for example, as follows.
A solid substance (sample) is placed in an apparatus (e.g. the type flow tester recommended by the society of Polymer Chemistry manufactured by Shimadzu Corporation) having a restricted outlet (e.g., a nozzle with an orifice diameter of 1 mm and a length of 10 mm) and capable of applying a predetermined load (e.g., 10 kg/cm2) to the sample by means of a plunger; when the sample is heated at a constant rate (e.g., 6xc2x0 C./min.) with the load kept applied thereto, the sample is eventually fluidized to start flowing out through the outlet.
This, in turn, causes the plunger to start lowering. When a graph is drawn with the amount of downward movement of the plunger taken on the vertical axis and the temperature taken on the horizontal axis, then an S-shaped curve will be drawn. If the height of the S-shaped curve (that is, the total amount of downward movement of the plunger between the time at which the sample starts flowing out and the time at which the sample stops flowing out) is h, the temperature at which the downward movement of the plunger becomes xc2xdh may be defined as the xc2xd-method temperature.
A toner composition according to still another aspect of the invention contains at least one kind of binder resin and has a gel percentage of 2 to 15%, a flow-out starting temperature of 80 to 120xc2x0 C., and a xc2xd-method temperature of 100 to 145xc2x0 C.
Since the toner composition according to the invention has a gel percentage that ranges between 2 and 15% (more preferably between 2 and 8%), it offers a sufficiently high strength and durability and is never crushed or softened to stick to a printer part during a print process, like the toner compositions according to above-mentioned one aspect and another aspect of the invention.
Furthermore, since the toner composition according to the invention is not brittle and thus can never crack during a print process.
In addition, the toner composition according to the invention has a flow-out starting temperature of 120xc2x0 C. or less and a xc2xd-method temperature of 145xc2x0 C. or less. Therefore, when printing is done on, for example, a transparent medium using the toner composition according to the invention, a toner layer formed has a smooth surface, exhibiting a high light transmission. The toner composition according to the invention is therefore excellent as a color toner used with a transparent medium.
Since the toner composition according to the invention has a flow-out starting temperature of 80xc2x0 C. or more and a xc2xd-method temperature of 100xc2x0 C. or more, toner melted during fusing can be prevented from sticking to a fusing roller. During any time other than fusing in an entire print process, the toner composition is not melted, making it easy to handle.
Furthermore, the toner composition according to the invention may contain at least one kind of dye. Namely, the toner composition can be of many different colors depending on the color of the dye to be included therein. Since the toner composition according to the invention develops a color by means of the dye, it is superior in color development performance and a range of color reproduction to conventional toner compositions that develop colors with pigments.
In addition to being capable of developing various colors as described in the foregoing, the toner composition according to the invention is superior in light transmission when printing is done on a transparent medium, it is suitable for color printing on OHP transparencies.
Typical dyes to be used include a direct dye, acid dye, disperse dye, cationic dye, reactive dye, sulfur dye, oil-soluble dye, and a metallic complex dye. Particularly preferable are the disperse dye and the cationic dye.
To give an example of a method of manufacturing a toner composition containing a dye, as disclosed in Japanese Patent Application Laid-Open Publication No. BEI 10-326029, the dye and resin particles are dispersed in an aqueous solvent and the solvent is agitated, while being heated to a temperature that can range between a softening temperature of the resin particles and a temperature 40xc2x0 C. higher than the softening temperature. After the resin particles are colored with the dye, they are subjected to reduction cleaning in order to remove excess dye that deposits on the surface of the resin particles. For a solvent used in this reduction cleaning, an aqueous solvent in which sodium hydrate or hydroxy sulfite is dissolved is to be used.
The toner composition according to the invention may be shaped in a spheres Namely, the toner composition has a high fluidity for its spherical shape and a low void ratio for a high bulk density thereof, minimizing heat loss during fusing.
The shape of the toner composition according to the invention may be represented by, for example, a sphericity (circularity) ranging between 1 and 0.95.
The sphericity (circularity) as the term used in this specification is one that, for example, is calculated through the following formula and the value is 1 if the shape is a true sphere. For measurement of sphericity, a flow type particle image analyzer FPIA-1000 manufactured by Sysmex may, for example, be used.
Sphericity (circularity)=L1/L2
where
L1: circumference of a circle having the same projection plane area as the particle image
L2: Length of outline of the particle projected image
The toner composition according to the invention is used as dry toner for electrostatic latent image developing.
Since the toner composition according to the invention has a sufficintly high strength and durability and is never crushed or softened to stick to a part inside a printer, making it right for dry toner for electrostatic latent image developing.
In the case where the toner composition according to the invention is used by injecting a charge controlling agent in a surface thereof in order to increase the amount of charge, the charge controlling agent and an externally added substance could never be embedded inside the toner composition for a high strength and durability thereof even when the composition is subjected to an external force repeatedly (e.g., a pressure applied by a printer roller and photoconductor) during a print process, which prevents the amount of charge of the toner composition from being decreased.
It therefore follows that, even after a continuous print cycle for printing a plurality of pages (that is, even after the toner composition has been subjected to a repeated external force inside the printer), there is no chance of the toner composition decreasing the amount of charge thereof. This results in, for example, the charge being distributed in a manner that it corresponds accurately to the distribution of charge on the surface of the photoconductor of the printer, enabling high-quality printing.
An organic finely divided powder and a charge controlling agent may be added to the toner composition according to the invention in order to make it easy to charge. As a method of applying such a substance, the resin particles, and the organic finely divided powder and charge controlling agent are mixed together by means of a mechanical impact force, thereby injecting the organic finely divided powder and charge controlling agent into the surface of the resin particles, as disclosed, for example, in Japanese Patent Application Laid-Open Publication No. HEI 11-65164.
Typical organic finely divided powders added to achieve the foregoing purpose include an acrylic resin finely divided powder, a fluorinated resin finely divided powder, a silicone resin finely divided powder, and a melamine resin finely divided powder.
Typical charge controlling agents include a metallic azo compound, a salicylic metal complex, a nigrosine, a triphenylmethane, and grade 4 ammonium salt.
The toner composition according to the invention is manufactured using a dispersion polymerization method that makes particles comprising at least one kind of binder resin. namely, since the binder resin particle made using the dispersion polymerization method has a small average particle diameter and a narrow particle diameter distribution, the toner composition according to the invention can have a small particle diameter and a narrow particle diameter distribution. Use of the toner composition according to-the invention-therefore makes printing of high image quality possible.
The dispersion polymerization method refers, for example, to the following. Namely, a monomer, a dispersing agent, initiator, and the like are loaded in a solvent and, when the solvent is set into a predetermined condition (e.g., a predetermined temperature), the initiator is made into a radical by which the monomer is polymerized to produce polymerized particles. At this time, a spot at which polymerization takes place is uniformly distributed throughout the solvent and a polymerization rate is constant regardless of the spot of polymerization thanks to an effect of the dispersing agent, which ensures that a large number of spherical polymerized particles of a uniform size are produced.
With the toner composition according to the invention, the toner layer formed when the toner composition is printed solidly and fused on a transparent medium has a gloss value of 30 or more and a surface roughness Rtm of 5 xcexcm or less,
In the case where the toner composition according to the invention is used on, for example, a printer employing the electrostatic latent image developing system to form a toner layer through printing solidly on a transparent medium, such toner layer has a gloss value of 30 or more and a surf ace roughness Rtm of 5 xcexcm or less, which means that a surface thereof offers a high smoothness.
Therefore, the toner layer formed by the toner composition according to the invention lets, for a high smoothness offered by a surface thereof, a large part of an incidence light pass therethrough without allowing it to disperse, thus offering an outstanding light transmission.
That is, since the toner composition according to the invention is capable of forming a toner layer offering a high light transmission on a transparent medium, it is good as a color toner used on the transparent medium. A typical transparent medium is OHP transparencies.
The gloss value is an index indicating a smoothness of a sample surface. Referring to FIG. 5, if the amount of light striking the sample is Io and the amount of light reflecting off the sample is II, then the gloss value is given by the following equations The higher the smoothness of the sample surface, the smaller the amount of light being dispersed and the higher the gloss value.
Gloss value (%)=(II/Io)xc3x97100
Solid printing refers to the following. With 256 gradation levels, for example, 16 grids each are theoretically arranged in a horizontal direction and a vertical direction, a total of 256 grids. Solid printing refers to printing on a mediium, in which a dot made up of the toner composition is present in each of all 256 grids. For example, in a 1,200-dpi, 256-gradation-level printer, one dot measures 21.2 xcexcm and one pixel measures about 339.2 xcexcm by 339.2 xcexcm.